public static void ScrollItem(ListViewBase control, int indexDelta)
{
if (control == null || control.Items == null)
return;
var scrollViewer = VisualTreeUtilities.GetVisualChild<ScrollViewer>(control);
var p = new Point(Window.Current.Bounds.Width/2, 10);
var transform = control.TransformToVisual(Window.Current.Content);
var checkPoint = transform.TransformPoint(p);
var q = from lvi in VisualTreeHelper.FindElementsInHostCoordinates(checkPoint, scrollViewer).OfType<ListViewItem>()
where lvi.Content != null
select lvi.Content;
var item = q.FirstOrDefault();
if (item == null)
return;
var index = control.Items.IndexOf(item);
var nextItemIndex = index + indexDelta;
if (index != -1 && nextItemIndex >= 0 && nextItemIndex < control.Items.Count)
{
var nextItem = control.Items[nextItemIndex];
control.ScrollIntoView(nextItem, ScrollIntoViewAlignment.Leading);
}
}
private static bool FocusIndex(ListViewBase listViewBase, int i)
{
var newContainer = listViewBase.ContainerFromIndex(i) as Control;
if (newContainer == null)
{
return false;
}
newContainer.Focus(FocusState.Keyboard);
listViewBase.ScrollIntoView(newContainer);
return true;
}
/// <summary>
/// Smooth scrolling the list to bring the specified index into view
/// </summary>
/// <param name="listViewBase">List to scroll</param>
/// <param name="index">The intex to bring into view</param>
/// <param name="itemPlacement">Set the item placement after scrolling</param>
/// <param name="disableAnimation">Set true to disable animation</param>
/// <param name="scrollIfVisibile">Set true to disable scrolling when the corresponding item is in view</param>
/// <param name="additionalHorizontalOffset">Adds additional horizontal offset</param>
/// <param name="additionalVerticalOffset">Adds additional vertical offset</param>
/// <returns>Note: Even though this return <see cref="Task"/>, it will not wait until the scrolling completes</returns>
public static async Task SmoothScrollIntoViewWithIndex(this Windows.UI.Xaml.Controls.ListViewBase listViewBase, int index, ItemPlacement itemPlacement = ItemPlacement.Default, bool disableAnimation = false, bool scrollIfVisibile = true, int additionalHorizontalOffset = 0, int additionalVerticalOffset = 0)
{
if (Math.Abs(index) > listViewBase.Items.Count)
{
throw new IndexOutOfRangeException("Index can't be greater than number of items in " + listViewBase.GetType().Name);
}
index = (index < 0) ? (index + listViewBase.Items.Count) : index;
bool isVirtualizing = default(bool);
double previousXOffset = default(double), previousYOffset = default(double);
var scrollViewer = listViewBase.FindDescendant <ScrollViewer>();
var selectorItem = listViewBase.ContainerFromIndex(index) as SelectorItem;
if (selectorItem == null)
{
isVirtualizing = true;
previousXOffset = scrollViewer.HorizontalOffset;
previousYOffset = scrollViewer.VerticalOffset;
var tcs = new TaskCompletionSource <object>();
void viewChanged(object s, ScrollViewerViewChangedEventArgs e) => tcs.TrySetResult(null);
try
{
scrollViewer.ViewChanged += viewChanged;
listViewBase.ScrollIntoView(listViewBase.Items[index], ScrollIntoViewAlignment.Leading);
await tcs.Task;
}
finally
{
scrollViewer.ViewChanged -= viewChanged;
}
selectorItem = (SelectorItem)listViewBase.ContainerFromIndex(index);
}
var transform = selectorItem.TransformToVisual((UIElement)scrollViewer.Content);
var position = transform.TransformPoint(new Point(0, 0));
if (isVirtualizing)
{
var tcs = new TaskCompletionSource <object>();
void viewChanged(object s, ScrollViewerViewChangedEventArgs e) => tcs.TrySetResult(null);
try
{
scrollViewer.ViewChanged += viewChanged;
scrollViewer.ChangeView(previousXOffset, previousYOffset, null, true);
await tcs.Task;
}
finally
{
scrollViewer.ViewChanged -= viewChanged;
}
}
var listViewBaseWidth = listViewBase.ActualWidth;
var selectorItemWidth = selectorItem.ActualWidth;
var listViewBaseHeight = listViewBase.ActualHeight;
var selectorItemHeight = selectorItem.ActualHeight;
previousXOffset = scrollViewer.HorizontalOffset;
previousYOffset = scrollViewer.VerticalOffset;
var minXPosition = position.X - listViewBaseWidth + selectorItemWidth;
var minYPosition = position.Y - listViewBaseHeight + selectorItemHeight;
var maxXPosition = position.X;
var maxYPosition = position.Y;
double finalXPosition, finalYPosition;
if (!scrollIfVisibile && (previousXOffset <= maxXPosition && previousXOffset >= minXPosition) && (previousYOffset <= maxYPosition && previousYOffset >= minYPosition))
{
finalXPosition = previousXOffset;
finalYPosition = previousYOffset;
}
else
{
switch (itemPlacement)
{
case ItemPlacement.Default:
if (previousXOffset <= maxXPosition && previousXOffset >= minXPosition)
{
finalXPosition = previousXOffset + additionalHorizontalOffset;
}
else if (Math.Abs(previousXOffset - minXPosition) < Math.Abs(previousXOffset - maxXPosition))
{
finalXPosition = minXPosition + additionalHorizontalOffset;
}
else
{
finalXPosition = maxXPosition + additionalHorizontalOffset;
}
if (previousYOffset <= maxYPosition && previousYOffset >= minYPosition)
{
finalYPosition = previousYOffset + additionalVerticalOffset;
}
else if (Math.Abs(previousYOffset - minYPosition) < Math.Abs(previousYOffset - maxYPosition))
{
finalYPosition = minYPosition + additionalVerticalOffset;
}
else
{
finalYPosition = maxYPosition + additionalVerticalOffset;
}
break;
case ItemPlacement.Left:
finalXPosition = maxXPosition + additionalHorizontalOffset;
finalYPosition = previousYOffset + additionalVerticalOffset;
break;
case ItemPlacement.Top:
finalXPosition = previousXOffset + additionalHorizontalOffset;
finalYPosition = maxYPosition + additionalVerticalOffset;
break;
case ItemPlacement.Centre:
var centreX = (listViewBaseWidth - selectorItemWidth) / 2.0;
var centreY = (listViewBaseHeight - selectorItemHeight) / 2.0;
finalXPosition = maxXPosition - centreX + additionalHorizontalOffset;
finalYPosition = maxYPosition - centreY + additionalVerticalOffset;
break;
case ItemPlacement.Right:
finalXPosition = minXPosition + additionalHorizontalOffset;
finalYPosition = previousYOffset + additionalVerticalOffset;
break;
case ItemPlacement.Bottom:
finalXPosition = previousXOffset + additionalHorizontalOffset;
finalYPosition = minYPosition + additionalVerticalOffset;
break;
default:
finalXPosition = previousXOffset + additionalHorizontalOffset;
finalYPosition = previousYOffset + additionalVerticalOffset;
break;
}
}
scrollViewer.ChangeView(finalXPosition, finalYPosition, null, disableAnimation);
}
